1. Field of the Invention
The present invention relates to a liquid crystal device having a composite layer or film which contains a liquid crystal phase of a liquid crystal material and a resin phase of resin as well as a method of manufacturing the same and a method of controlling the form of the resin phase in the liquid crystal device.
2. Description of the Background Art
Various kinds of liquid crystal display devices having a memory effect have already been proposed.
U.S. Pat. No. 3,578,844 has disclosed that a memory effect is exhibited by a liquid crystal device, in which cholesteric liquid crystal material capsuled with a polymer such as gelatin or gum arabi is held between a pair of substrates. It has also been disclosed that such a liquid crystal device exhibits three different appearances when no voltage is applied, when a voltage is applied and when voltage application is stopped.
National Patent Publication of Translated Version No. 6-507505 (JP, A, 6-507505) has disclosed that a memory effect is exhibited by a liquid crystal device, in which a chiral nematic liquid crystal material containing resin added thereto at a rate of 10% by weight with respect to the whole weight and exhibiting a cholesteric characteristic is held between a pair of substrates. It has also disclosed that such a liquid crystal device exhibits different appearances according to orientations, i.e., a planar orientation in which helical axes of liquid crystal molecules are oriented vertically with respect to the substrate surface and a focal conic orientation in which the helical axes are oriented irregularly or substantially parallel to the substrate surface.
If the helical axes in the planar orientation are oriented excessively uniformly, a dependency on a viewing angle excessively increases and, for example, the liquid crystal device, which exhibits a transparent appearance when viewed vertically with respect to the substrate, exhibits an opaque appearance when viewed in an angle shifted from the vertical direction with respect to the substrate. According to the foregoing publication No. 6-507505, however, addition of a small amount of resin into the liquid crystal material causes a mutual action between the liquid crystal material and the resin at a region near the resin, and thereby the liquid crystal material near the resin exhibits a lower response to an applied electric field, compared with the liquid crystal material remote from the resin so that the dependency on the viewing angle is improved.
A liquid crystal device including cholesteric liquid crystal material and resin does not require a polarizer because it utilizes selective reflection of incident rays by the liquid crystal material. Also, formation of cells is not required. Therefore, the liquid crystal device can perform bright display on a large area. Since this liquid crystal device has a memory effect, memory elements such as TFT, MIM are not required.
According to the above method in which a small amount of resin is added to the liquid crystal material, however, a self-holding property or form-keeping property cannot be achieved sufficiently because the amount of the added resin is small. Therefore, a state of display is liable to change due to a pressure applied to the substrate surface.
Although this problem can be avoided by increasing an amount of the added resin, this causes other problems such as an increase of the required drive voltage and a lowering of the contrast.
Meanwhile, Japanese Laid-Open Patent Publication No. 6-301015 (301015/1994) has disclosed a liquid crystal device having a composite layer which includes resin partitions each formed between picture elements as well as liquid crystal regions formed between the partitions. This partition structure is formed in such a manner that a solution of a liquid crystal material and a raw material of resin is radiated with ultraviolet rays through a photomask so that a portion of the raw material of resin radiated with ultraviolet rays is cured to form a resin partition which corresponds to the photomask.
The liquid crystal device having the partition structure of resin can suppress flow of the liquid crystal material, and therefore has a high self-holding property. Further, the forms of the liquid crystal regions can be uniform and can be positioned accurately. Therefore, required drive voltages for the respective liquid crystal regions can be uniform so that it is possible to reduce the drive voltage required for operating simultaneously all the liquid crystal regions. Since each liquid crystal region has a relatively large size defined by the partition structure, the device can provide a better contrast than a liquid crystal device in which fine liquid crystal regions are dispersed in the resin portions. Such an advantage can also be achieved that sealing is not required at the periphery of the substrate.
Japanese Laid-Open Patent Publication No. 6-301015 has also disclosed that the resin partition structure can employ a network-form structure, in which a slight amount of liquid crystal material is finely dispersed in the resin, and can also employ a structure, in which the liquid crystal material is not contained in the resin and the network form is not formed. The above publication has also disclosed that the dependency on the viewing angle can be reduced by orientation processing using homogeneous orientation film or the like when using twisted nematic (TN) or super-twisted nematic (STN) liquid crystal.
In the liquid crystal device having the resin partition structure, the liquid crystal material which is dispersed finely within the resin tends to scatter the light and, thereby reducing the contrast even though the resin in the network form can reduce the dependency on the viewing angle in the planar orientation state of the liquid crystal material. If the resin wall does not have a network form, the contrast can be good, but the dependency on the viewing angle increases because the helical axes of cholesteric liquid crystal molecules in the planar orientation are oriented too uniformly. In this case, the dependency on the viewing angle can be reduced by disarranging the orientation of the helical axes of liquid crystal molecules with the orientation processing. However, if cholesteric liquid crystal material has a short helical pitch length, the orientation processing can exert only a small influence on the orientation of liquid crystal molecules, and therefore cannot sufficiently reduce the dependency on the viewing angle.
Accordingly, it is desired to control the form of the resin wall so that both the contrast and the dependency on the viewing angle may be improved. According to a polymerization phase separating method, the form and structure of the resin wall changes widely depending on the conditions of the phase separation and the kinds of resin and liquid crystal material. Furthermore, it cannot be controlled easily. The contrast of the liquid crystal device is affected in a complicated manner by the structure of the resin wall, as well as a consistency of reflectance between the liquid crystal material and the resin, a mechanism of phase separation and others. Accordingly, if the resin wall is formed in a desired form while other conditions are satisfied, the materials of the liquid crystal and resin which can be used are restricted to a narrow range. A resin wall may be formed in advance on one of the substrates by a screen printing method, ink jet or the like. However, finer picture elements and therefore high resolution display elements can be formed when the resin wall is formed by the polymerization phase separating method.